In "baseline dimensioning" a set of dimensions are all calculated/stated as distances from a single origin, instead of from each-other.This can be a useful way of avoiding "tolerance build-up" ... Think of a row of holes, supposedly 20mm apart; and compare the accuracy of positioning with a tolerance of [say] +/- 0.5mm ... The tenth hole could be out-of-position by 5mm if they are dimensioned from each other, but only by 0.5mm if individually dimensioned from a common baseline.